DSpace at VNU: Rhenium and technetium complexes with tridentate S,N,O ligands derived from benzoylhydrazine

Polyhedron 28 (2009) 3945–3952

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Polyhedron
journal homepage: www.elsevier.com/locate/poly

Rhenium and technetium complexes with tridentate S,N,O ligands derived from
benzoylhydrazine
Hung Huy Nguyen a,1, Ulrich Abram b,*
a
b

Department of Chemistry, Hanoi University of Sciences, 19 Le Thanh Tong, Hanoi, Viet Nam
Institute of Chemistry and Biochemistry, Freie Universität Berlin, Fabeckstr. 34-36, D-14195 Berlin, Germany

a r t i c l e

i n f o

Article history:
Received 25 August 2009
Accepted 14 September 2009
Available online 29 September 2009
Keywords:
Rhenium
Technetium
Mixed-ligand complexes
Benzoylthioureas
X-ray structure

a b s t r a c t
A potentially tridentate ligand with an S,N,O donor set, H2L, is formed by the reaction of N-[(diethylaminothiocarbonyl)benzimidoyl chloride with benzoylhydrazine. Reactions of H2L with (NBu4)[MOCl4] complexes (M = Re, Tc) give five-coordinate, neutral oxo complexes of the composition [MOCl(L)].
Mixed-ligand complexes of rhenium(V) containing the tridentate L2À ligand and bidentate N,N-dialkylN0 -benzoylthioureato ligands (R2btuÀ) are formed in high yields when (NBu4)[ReOCl4] is treated with
mixtures of H2L and HR2btu. Another approach to the mixed-ligand products is the reaction of [ReOCl(L)]
with an equivalent amount of HR2btu.
Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction
The widespread use of the radionuclide 99mTc in diagnostic nuclear medicine and the potential of the b-emitting radioisotopes
186
Re and 188Re in radiotherapy cause a continuing interest in the
coordination chemistry of technetium and rhenium [1,2]. In this
context, there is a permanent need for efficient chelating systems.
Ligands, which are suitable for the stabilization of the {MV@O}3+
cores (M = Re, Tc) are of particular interest, since reduction of
[MO4]À ions from the commercial generator systems with common
reducing agents frequently form oxometallates(V). Ligand systems,
which stabilize this core under physiological conditions are tetradentate N,S,O chelators [3,4]. However, the tuning of the biological
properties of the resulting complexes by variations in the periphery of the ligands is difficult and sometime results in the formation
of different stereoisomers [4]. Mixed-ligand approaches give access
to a smooth tuning of the ligand properties and, thus, of their biological behavior.
Following the so-called mixed-ligand concept, many ‘3+1’ systems, which are neutral complexes with a [MO]3+ core and a
mixed-ligand set of a dianionic tridentate ligand containing one
or more sulfur donor atoms, such as [SSS], [SOS], [SNS], [SNN], or
[ONS], and a monodentate thiolate were studied [5]. Finally, it

* Corresponding author. Tel.: +49 30 838 54002; fax: +49 30 838 52676.
E-mail address: (U. Abram).
1
Present address: Institute of Chemistry and Biochemistry, Freie Universität Berlin,

Fabeckstr. 34-36, D-14195 Berlin, Germany.
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.09.012

was found that many of these ‘3+1’ complexes were relatively
unstable in vitro and in vivo due to a ready substitution of the labile
monothiolate RSÀ by physiological thiols such as cysteine or glutathione [6]. Generally, this may be explained by the 16 valence electron nature of the five-coordinate ‘3+1’ complexes. Replacement of
the labile monothiolate by bidentate ligands results in so-called
‘3+2’ systems with a closed-shell electron configuration and, thus,
a higher stability is expected [7]. Several ‘3+2’ mixed-ligand complexes with ligands carrying different donor sets such as [SNS]/
[PO] [7], [NOS]/[NO] [8], [NOS]/[NN] [9], [NON]/[OO] [10], [NOS]/
[SN] [11] or [ONO]/[PO] were studied [12]. Some of them show
interesting properties, which encourage further studies and the
introduction of hitherto not regarded ligand systems in such
considerations.
In previous papers, we described synthesis and characterization
of a new class of tridentate N-(dialkylaminothiocarbonyl)benzamidine ligands (H2R2tcba) which form stable, five-coordinate complexes of the composition [ReOCl(R2tcba)] (1) [13], and
elucidated the coordination chemistry of N,N-dialkyl-N0 -benzoylthioureas, HR2btu, with rhenium and technetium (Scheme 1)
[14]. The advantage of these two ligand classes is the convenience
of modifications in the periphery of their chelating system. This allows the variation of fundamental properties of the products such
as solubility, polarity and lipophilicity and also gives access to bioconjugation via the periphery of the tridentate ligands. With complexes of the types 1 and 2, appropriate starting materials are
available with the bidentate and tridentate ligands already in coordination positions, which are expected for the intended mixedligand compounds, and we could show that stable mixed-ligand


3946

H.H. Nguyen, U. Abram / Polyhedron 28 (2009) 3945–3952

R1
N

N

NH

R2

S

O

OH

Et

R3

H
N

N

N

R4

S
HR2btu

Cl

N

N

O

O

Cl

Re
O

R2

R3

S

Cl

N
N

S

Re

R4

Cl

O
1

2
R1

N

N

R2

S

M

R3

S
O

NH

N

Et

S
H2L

Scheme 2. Synthesis of H2L.

R1

O

HN

R3, R4 = alkyl or aryl

Ph3P

N

- Et3N.HCl

N

O

R1R2 = Et2 or Morph

O

Et

S

Et2tcbCl

H2R2tcba

N

N

Et

PhCONHNH2
Et3N, Me2CO

3

N
N

R4
M = Re, Tc

Scheme 1. Related ligands and hitherto known rhenium complexes.

complexes of the composition [MO(R2tcba)(R2btu)] (M = Re, Tc) (3)
can readily be prepared [15].
In extension of this work, we synthesized a novel tridentate ligand, H2L, by the reaction of N-(diethylaminothiocarbonyl)benzimidoyl chloride (R2tcbCl) with benzoylhydrazine and studied
its reaction patterns with common rhenium and technetium
complexes.

can readily be checked by thin-layer chromatography and is conveniently indicated by the formation of a colorless precipitate of
NEt3ÁHCl, which is almost insoluble in acetone.
The IR spectrum of H2L is characterized by absorptions of the
NH stretches at 3225 and 3163 cmÀ1 and a very strong absorption
at 1655 cmÀ1, which can be assigned to the C@O vibration. The 1H
NMR spectrum reflects the hindered rotation around the C–NEt2
bond, which is typically indicated by broad singlet signals corresponding to the ethyl residues. This has also been found for other
thiocarbamoylbenzamidines [13,15–18].
Fig. 1 illustrates the structure of H2L together with the intramolecular hydrogen bond between the nitrogen atom of the
benzoylhydrazone unit and the sulfur atom. An additional intermolecular hydrogen bond is established between N3 and O57. Selected bond lengths and angles are summarized in Table 1. The
positions of the hydrogen atoms at the atoms N3 and N59 are indicated by peaks of electron density in the final Fourier maps of the
structure refinement and the fact that they are involved in hydrogen bonds. This finding is also consistent with the bond lengths of
the C–N bonds in the ligand framework, in which the C4–N5 bond
of 1.266(4) Å is within the expected range of a C@N double bond
and the C4–N3 distance of 1.431(4) Å is a typical C–N single bond.
This is in perfect agreement with structure C of Scheme 3 and a
description as a benzoylhydrazone. Such a bonding situation is
hitherto without precedence for the thiocarbamoylbenzamidines
under study. In corresponding structures, such as derivatives with
aromatic amines [13] or thiosemicarbazones [17], a hydrogen atom

2. Results and discussion
2.1. Synthesis and structure of H2L
Reactions of N-(N0 ,N0 -dialkylaminothiocarbonyl)benzimidoyl
chlorides with primary amines have been shown to be a convenient approach for the synthesis of bidentate S,N ligands [16] or
tridentate S,N,O, S,N,N or S,N,S chelators [13,17]. The coordination
behavior of the obtained ligands strongly depends on the amines
used, since they significantly influence the basicity of the N donor
position and the denticity of the resulting ligand system. While the
coordination chemistry of the bidentate ligands has been studied

with a variety of metal ions [18], the tridentate systems have hitherto only be used for the formation of rhenium and technetium
complexes [13,17].
The novel benzoylhydrazine derivative H2L is formed by the
reaction of N-(N0 ,N0 -diethylaminothiocarbonyl)benzimidoyl chloride and benzoylhydrazine. In the presence of the supporting base
NEt3, the reaction proceeds quickly and under mild conditions. The
product can be isolated as colorless, microcrystalline, analytically
pure solid in high yields (Scheme 2). The progress of the reaction

Fig. 1. Molecular structure of H2L. Thermal ellipsoids represent 50% probability
[23].

Table 1
Selected bond lengths (Å) in H2L.
S1–C2
C2–N3
C2–N6
N3–C4

1.694(4)
1.373(4)
1.335(4)
1.431(4)

C4–N5
N5–N59
N59–C58
C58–O57

1.266(4)
1.383(4)

1.376(4)
1.222(4)


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H.H. Nguyen, U. Abram / Polyhedron 28 (2009) 3945–3952

R2

R1
N

H
N

N
S

Ph

O
N
H

Ph

R2

R1

N
S

A
1

2

R

R
N

S

N
Ph

Ph

N
H

R2

R
N

N

Ph

Ph

O
N
SH

N
Ph

N
H

Ph

R2

E

OH

H
N
S
D

C
R2

OH

B
1

O

H
N

R1
N

H
N

N

R1
N

N

Ph

N

Ph
OH
N

SH

N

N

Ph

Ph

F

Fig. 2. Molecular structure of [TcOCl(L)] (4). Thermal ellipsoids represent 50%
probability [23]. H atoms are omitted for clarity.

Scheme 3. Conformers of H2L.

locates on the nitrogen atom N5 and a double bond is established
between C4 and N3. It can also not be excluded that in solution
and/or in metal complexes of the compound the other conformers
of Scheme 3 play a considerable role.

2.2. [MOCl(L)] complexes (M = Tc, Re)
The reaction of H2L with the common technetium(V) precursor
(NBu4)[TcOCl4] in methanol at room temperature gives rapidly a
red solid of the composition [TcOCl(L)] (4) (Scheme 4). The infrared
spectrum of complex 4 exhibits a strong bathochromic shift of the
mC@O band of about 150 cmÀ1, together with the disappearance of
absorptions in the region above 3150 cmÀ1, which correspond to

mNH stretches in the uncoordinated H2L. Both results indicate chelate formation with a large degree of p-electron delocalization
within the chelate rings and the expected double deprotonation
of the ligand. An intense band appearing at 976 cmÀ1 can be assigned to the Tc@O vibration [19]. The 1H NMR spectrum provides
additional evidence for the proposed composition and molecular
structure of the complex. The rotation around the C–NEt2 bond
in 4 is more restricted than that in the uncoordinated H2L. This is
reflected by two sets of well resolved signals corresponding to
the methyl groups. The corresponding signals of the methylene
protons are sparingly resolved and appear as a broad signal.
Fig. 2 depicts the molecular structure of compound 4 as a prototype compound for these types of complexes. Selected bond
lengths and angles are listed in Table 2. The technetium atom possesses a distorted square–pyramidal coordination environment
with an oxo ligand in the apical position and the square plane
formed by the donor atoms of the tridentate ligand and the chloro
ligand. This square plane is slightly distorted, with a main deviation of 0.097(1) Å from a mean least-square plane for atom O57.
The Tc atom is situated by 0.691(1) Å above the basal plane towards the oxo ligand. All O10–Tc–X angles (X = equatorial donor

Table 2
Selected bond lengths (Å) and angles (°) in [TcOCl(L)] (4) and [ReOCl(L)](5).

M–O10
M–Cl
M–S1
M–N5
M–O57
S1–C2
C2–N3
O10–M–Cl
O10–M–S1
O10–M–N5
O10–M–O57

S1–M–N5

4

5

1.644(2)
2.3356(6)
2.2878(6)
1.994 (2)
1.970(1)
1.756(2)
1.335(3)
108.03(6)
108.62(6)
107.08(7)
111.92(7)
89.99(5)

1.647(9)
2.349(3)
2.276(3)
1.972(9)
1.967(7)
1.74(1)
1.36(1)
110.0(4)
108.1(3)
107.9(5)
112.5(4)

91.4(2)

4

5

C2–N6
N3–C4
C4–N5
N5–N59
N59–C58
C58–O57

1.333(3)
1.317(3)
1.351(3)
1.409(2)
1.281(3)
1.340(2)

1.34(1)
1.30(1)
1.37(1)
1.43(1)
1.28(1)
1.33(1)

S1–M–O57
S1–M–Cl
N5–M–O57

N5–M–Cl
O57–M–Cl

139.45(4)
82.92(2)
77.57(6)
144.63(5)
85.55(4)

139.4(2)
84.5(1)
76.3(3)
141.2(3)
82.0(2)

atom) fall in the range between 107° and 112°. This is in good
agreement with the typical bonding situation of square–pyramidal
TcVO complexes [19]. The Tc@O distance of 1.644(2) Å is within the
expected range of a technetium–oxygen double bond [19]. Despite
the fact that the six-membered ring formed by Tc, S1, C2, N3, C4
and N5 is not planar with a maximum distortion from the mean
least-square plane of 0.263(1) Å for the Tc atom, a reasonable
delocalization of p-electrons is observed. Consequently, the C–S
and C–N bonds inside the chelate ring possess partially double
bond character. The bonding situation in the five-membered chelate ring is similar to those in typical benzoylhydrazone complexes
with shortened C58–N59 and lengthened C58–O57 bonds, being
both in the range between carbon–nitrogen and carbon–oxygen
single and double bonds.
The reaction of H2L with (NBu4)[ReOCl4] is much slower than
that with the analogous technetium starting material. The ligand

exchange product of the composition [ReOCl(L)] (5) can be isolated
after a period of several hours as red, microcrystalline solid directly
from the reaction mixture in good yield. Addition of a supporting

Et
O
Cl
Cl

M

Cl

N

-

Cl

M = Re, Tc

+

HN

NH

N
S

Et
Et

N
+ NEt3, MeOH
- (HNEt3)Cl

N

O

O

S

M
O

(4) M = Tc
Scheme 4. Synthesis of [MOCl(L)] complexes.

N

N

Cl
(5) M = Re

Et

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H.H. Nguyen, U. Abram / Polyhedron 28 (2009) 3945–3952

base like NEt3 accelerates the rate of the reaction, but results in the
formation of side-products, which are mainly formed by solvolysis
of the complex 5. The IR spectrum of 5 reveals a m(Re@O) frequency
at 991 cmÀ1 [19] and a strong bathochromic shift of the C@N band
as a consequence of the complex formation. The 1H NMR spectrum
of 5 is very similar to that of 4, except that the resolution of the
methylene proton signals is much better than in the spectrum of
the technetium compound and four overlapping multiplet signals
with ABX3 coupling patterns of CH2 protons can be identified in
the region between 3.9 and 4.1 ppm. In the 13C NMR spectrum of
5, the separated signals of two ethyl groups are also observed
due to the hindered rotation. The resonances assigned for
C@N, C@S and C@O, respectively, appear at 166.69, 172.70 and
173.73 ppm.
The molecular structure of 5 is virtually identical with that of its
technetium analogue. Therefore, no extra figure is given for this
compound. Selected bond lengths and angles are compared with
the corresponding values of 4 in Table 2. The atomic numbering
scheme of Fig. 2 has also been applied for the rhenium compound.
As discussed for technetium compound 4, the metal atom in 5 has
a distorted square–pyramidal coordination sphere and is located
0.691(1) Å above the equatorial plane formed by S1, N5, O57 and
Cl. The Re–O distance of 1.647(9) Å is within the typical range of
a rhenium–oxygen double bond [19]. All other structural features
discussed above for the technetium complex holds also true for

the rhenium analogue.
2.3. Mixed-ligand complexes of the composition [ReO(L)(R1R2btu)]
Mixed-ligand complexes of the composition [ReO(L)(R1R2btu)]
(6) can be synthesized by two different routes (Scheme 5). The first
approach concerns a two-step synthesis, in which 5 is used as the
starting compound. This labile square–pyramidal complex is treated with equimolar amounts of benzoylthioureas in warm CH2Cl2/
MeOH and the mixed-ligand complexes are obtained in high yields.
The complexes 6 can alternatively be prepared in one-pot reactions from (NBu4)[ReOCl4] and stoichiometric amounts of the tridentate benzamidine and bidentate benzoylthioureas. The yields
of such reactions are not significantly lower than those obtained
from the two-step procedure. When the ligands are added subsequently, the supporting base should be added a few minutes after

Et
N
N

N

O

N

(TBA)[ReOCl4]

(5)

Re
O

Et

S
Cl

HR1R2btu,H2L,
Et3N

1 2

HR R btu, Et3N
Et
N
N

N

O

N

Et

S

Re
R1

S

O
O

N
N

(6)

R2

a: R1 = R2 = Ph
b: NR1R2 = morpholinyl

Scheme 5. Synthesis of the mixed-ligand complexes.

the addition of the second ligand in order to avoid undesired sidereactions. The products are readily soluble in CH2Cl2, but sparingly
soluble in MeOH. Single crystals of good quality are obtained by
slow evaporation of CH2Cl2/MeOH mixtures of the complexes.
Infrared spectra of complexes 6 do not show any absorption in
the regions above 3100 cmÀ1, which indicates the expected double
deprotonation of benzamidines and the single deprotonation of the
benzoylthiourea ligands during complex formation. Additionally,
the sharp intense absorptions in the range between 1620 and
1690 cmÀ1, which are assigned to the mC@N and mC@O stretches in
the spectra of the non-coordinated benzamidines and benzoylthioureas shift to the range between 1500 and 1540 cmÀ1
and appear as broad bands. Intense bands each at 972 cmÀ1 are assigned to the Re@O stretches [19]. They appear about 20 cmÀ1
bathochromically shifted with respect to the corresponding
absorption in 5.
Because of the hindered rotation around the C–NR2 bonds and
the rigidity of the tertiary amine nitrogen atoms in both the benzamidine and benzoylthiourea ligands, the 1H NMR spectra of 6
are complicate. Especially for complex 6b, the rigidity of the morpholinyl moiety in the coordinated morphbtuÀ ligand makes all
eight protons of the morpholine ring magnetically inequivalent.

This is indicated by four well resolved multiplet signals with ABXY
splitting patterns at 4.29, 4.34, 4.46 and 4.58 ppm of four different
CH2–O protons and four CH2–N protons appear in two multiplet
signals at 3.74 and 3.89 ppm. The 13C NMR spectra of the complexes 6 are more simple, since they are only influenced by hindered rotation around the C–NR2 bonds. As the consequence, two
separated signals for each CH2 and CH3 carbon atoms in NEt2
groups and/or CH2–N and CH2–O atoms of the morpholinyl moiety
are observed. The chemical shifts of the aromatic carbon atoms,
which can not be unambiguously assigned, are in the range between 127 ppm and 136 ppm. Resonances of the carbon atoms of
the C@X groups (X = N, O, S) appear in the range from 163 ppm
to 187 ppm. The very similar structures between benzoylthioureas
and thiocarbamoylbenzamidines produce difficulties in the assignment of the C@X signals in the 13C NMR spectra of the complexes.
Nevertheless, with respect to their analogous coordination sphere,
the chemical shifts of the C@N, C@S and C@O signals of (L)2À in the
two complexes should be essentially the same and appear at
163 ppm, 174 ppm and 176 ppm. FAB+ mass spectra of the
mixed-ligand complexes 6 show intense peaks of the molecular
ions with the expected isotopic patterns. Interestingly, fragments
which result from the loss of R1R2NC„N residues of the R1R2btuligand appear in all spectra as intense signals.
The molecular structures of 6a and 6b are depicted in Fig. 3. Selected bond lengths and angles are given in Table 3. In these structures, the rhenium atoms exhibit distorted octahedral coordination
environments. Axial positions are occupied by terminal oxo ligands
and the oxygen atoms of the bidentate R1R2btuÀ ligands. The tridentate thiocarbamoylbenzamidine ligands coordinate meridional
and the remaining position of the equatorial coordination sphere is
occupied by the sulfur atom of the R1R2btuÀ ligand. The metal
atoms are located slightly above the mean least-square planes
formed by the atoms S1, N5, O57 and S12 toward the oxo ligand
with a distance of 0.410(2) Å for 6a and 0.381(3) Å for 6b. The
Re@O distances of 1.644(8) and 1.659(7) Å are in the expected
range of rhenium–oxygen double bonds.
A remarkable structural feature in complexes 6 is the coordination of the benzoylic oxygen atoms trans to the oxo ligands. The
Re–O15 bonds of 2.219(7) and 2.249(6) Å are at the upper limit

of trans-O@Re–O single bond lengths in Re(V) oxo complexes. Similar values have previously been reported only for some complexes
with small monodentate neutral ligands such as H2O, MeOH or
Me2CO [19]. However, the C14–O15 bonds are not significantly
shorter than corresponding distances in R1R2btuÀ ligands in other


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H.H. Nguyen, U. Abram / Polyhedron 28 (2009) 3945–3952

rhenium complexes [14]. All Re–S11 and C12–S11 bond lengths are
in the typical range of Re–S single bonds and CAS bonds with partially double bond character as has been previously reported for
oxorhenium(V) complexes with a variety of benzoylthiourea ligands [19]. In the benzamidine moiety, the Re–S1 and Re–N5 bond
distances are lengthened by about 0.03–0.06 Å compared to the
values in 5. Additionally, the Re–S1 bonds are by about 0.06 Å
shorter than the Re–S11 bonds which are in their cis positions.
While the two chelate rings of the benzamidine ligands are almost
planar, the six-membered rings of the benzoylthioureas are dramatically distorted. This is mainly due to the large deviations of
the Re atoms of 1.448(6) Å (compound 6a) and 1.483(8) Å (compound 6b) from the least-square planes formed by the other atoms
of the chelate rings. Nevertheless, a considerable delocalization of
p-electron density inside the chelate rings is observed for both the
benzoylthiourea and the benzamidine ligands. This is mainly indicated by the observation of almost identical bond lengths for all
C–N bonds, which fall within the range between C–N single and
double bonds. The bond length equalization is also extended to
the C2–N6 and C12–N16 bonds (1.33–1.36 Å), which are clearly
shorter than expected for C–N single bonds. The partial transfer
of electron density into these bonds well agrees with the 1H
NMR spectra of the compounds, which indicate a rigid arrangement of –NR1R2 moieties.
3. Conclusions
We could demonstrate that the tridentate ligand H2L readily

forms five-coordinate technetium and rhenium complexes of the
composition [MOCl(L)]. The remaining chloro ligand is labile and
can readily be replaced by bidentate chelators such as N,N-dialkyl-N0 -benzoylthioureas. The resulting mixed-ligand complexes
can also be prepared in one-pot reactions starting from (NBu4)
[ReOCl4] and mixtures of H2L and benzoylthioureas.
The presented study on prototype compounds is the experimental basis of ongoing studies in our laboratory which deal with
ligands of the same type, which contain anchor groups for the conjugation to peptides or proteins.
4. Experimental
4.1. Materials
Fig. 3. Molecular structures of (a) [ReO(L)(Ph2btu)] (6a) and (b) [ReO(L)(morphbtu)} (6b). Thermal ellipsoids represent 50% probability [23]. H atoms are
omitted for clarity.

All reagents used in this study were reagent grade and used
without further purification. Solvents were dried and freshly
distilled prior use unless otherwise stated. (NBu4)[ReOCl4],

Table 3
Selected bond lengths (Å) and angles (°) in [ReO(L)(Ph2btu)] (6a) and [ReO(L)(morphbtu)] (6b).

Re–O10
Re–S1
Re–N5
Re–O57
Re–O15
Re–S11
O10–Re–Sl
O10–Re–S11
O10–Re–N5
O10–Re–O57
O10–Re–O15

O57–Re–N5
O57–Re–S1
O57–Re–S11

6a

6b

1.659(7)
2.313(2)
2.041(7)
2.043(5)
2.249(6)
2.391(2)
103.3(3)
101.6(3)
102.1(3)
95.7(3)
172.1(3)
78.1(3)
160.8(2)
92.2(2)

1.644(8)
2.327(3)
2.020(9)
2.052(7)
2.214(7)
2.403(3)
102.8(3)

98.5(3)
102.8(4)
96.0(3)
169.9(3)
77.8(3)
160.5(2)
96.3(2)

6a

6b

S1–C2/S11–C12
C2–N3/C12–N13
N3–C4/N13–C14
C4–N5/C14–O15
C2–N6/C12–N16

1.75(1)/1.770(9)
1.36(1)/1.34(1)
1.31(1)/1.32(1)
1.32(1)/1.263(9)
1.36(1) /1.35(1)

1.77(1)/1.75(1)
1.33(2)/1.34(1)
1.34(1)/1.32(1)
1.32(1)/1.27(1)
1.32(1)/1.33(1)

O57–Re–O15
N5–Re–S1
N5–Re–S11
N5–Re–O15
S1 –Re–S11
S1 –Re–O15
S11 –Re–O15

76.6(2)
94.5(2)
155.1(2)
77.8(2)
87.26(9)
84.5(1)
77.7(2)

75.3(3)
92.7(3)
158.4(3)
80.7(3)
86.3(1)
86.4(2)
77.7(2)


3950

H.H. Nguyen, U. Abram / Polyhedron 28 (2009) 3945–3952

(NBu4)[TcOCl4] [20] were prepared by published methods.

HR1R2btu ligands [21] and N-(diethylaminothiocarbonyl)benzimidoyl chloride [16] were synthesized by the standard procedures
of Beyer et al.
4.2. Radiation precautions
99

Tc is a weak bÀ-emitter. All manipulations with this isotope
were performed in a laboratory approved for the handling of radioactive materials. Normal glassware provides adequate protection
against the low-energy beta emission of the technetium compounds. Secondary X-rays (bremsstrahlung) play an important role
only when larger amounts of 99Tc are used.
4.3. Physical measurements
Infrared spectra were measured as KBr pellets on a Shimadzu
FTIR-spectrometer between 400 and 4000 cmÀ1. ESI mass spectra
were measured with an Agilent 6210 ESI-TOF (Agilent Technologies). All MS results are given in the form: m/z, assignment. Elemental analysis of carbon, hydrogen, nitrogen, and sulfur were
determined using a Heraeus vario EL elemental analyzer. The
99
Tc values were determined by standard liquid scintillation counting. NMR-spectra were taken with a JEOL 400 MHz multinuclear
spectrometer.
4.4. Synthesis of the ligand H2L
chloride
N-(N0 ,N0 -Diethylaminothiocarbonyl)benzimidoyl
(1.227 g, 5 mmol) was dissolved in 10 mL dry acetone and slowly
added to a stirred mixture of benzoylhydrazine (680 mg, 5 mmol)
and NEt3 (1.51 g, 15 mmol) in 10 mL of dry acetone. The mixture
was stirred for 4 h at room temperature. The formed precipitate
of NEt3ÁHCl was filtered off and the filtrate was evaporated under
reduced pressure. The residue was re-dissolved in 10 mL CH2Cl2
and extracted two times with brine solution (2 Â 10 mL). The organic phase was dried over MgSO4 and evaporated under reduced
pressure to dryness. The resulting residue was treated with diethylether (15 mL) and stored at À20 °C for 24 h. The crude product
was filtered off, dried under vacuum and recrystallized from
CH2Cl2/n-hexane. Yield: 56% (0.991 g). Anal. Calc. for C19H22N4OS:

C, 64.38; H, 6.26; N, 15.81; S, 9.05. Found: C, 64.51; H, 6.42; N,
15.62; S, 9.00%. IR (m in cmÀ1): 3225(m), 3163(m), 3043(m),
2931(m), 1655(vs), 1542(vs), 1504(vs), 1481(vs), 1261(s),
1142(m), 1072(m), 1026(m), 779(m), 713(s), 694(s).1H NMR
(CDCl3; d, ppm): 0.92 (s, br, 3H, CH3), 1.00 (s, br, 3H, CH3), 3.40
(s, br, 2H, CH2), 3.76 (s, br, 2H, CH3), 7.36–7.48 (m, 6H, Ph), 7.77
(d, J = 7.2 Hz, 2H, Ph), 7.84 (d, J = 7.4 Hz, 2H, Ph).

7.50 (t, J = 7.3 Hz, 1 H, Ph), 7.84 (d, J = 7.9 Hz, 2 H, Ph), 8.01 (d,
J = 8.1 Hz, 2 H, Ph).
4.5.2. [ReO(L)Cl] (5)
The red microcrystalline 5 was prepared from (NBu4)[ReOCl4]
and H2L by a similar procedure as described for 4, except that
the reaction time was increased and the precipitation of the product was finished only after 6 h. Yield: 61% (36 mg). Anal. Calc. for
C19H20ClN4O2SRe: C, 38.67; H, 3.42; N, 9.49; S, 5.43. Found: C,
38.47; H, 3.50; N, 9.41; S, 5.22%. IR (m in cmÀ1): 3055(w),
2989(w), 2932(w), 1508(vs), 1438(m), 1389(m), 1326(m),
1292(m), 1145(w), 1072(w), 1026(w), 991(s), 775(m), 709(m),
691(s). 1H NMR (CDCl3, d, ppm): 1.33 (t, J = 7.1 Hz, 3H, CH3), 1.39
(t, J = 7.1 Hz, 3H, CH3), 3.90 (m, 2H, CH2), 4.12 (m, 2H, CH2), 7.32
(t, J = 7.2 Hz, 2H, Ph), 7.38 (t, J = 7.0 Hz, 1H, Ph), 7.43 (t, J = 7.5 Hz,
2H, Ph), 7.51 (t, J = 7.4 Hz, 1H, Ph), 7.85 (d, J = 7.9 Hz, 2H, Ph),
8.05 (d, J = 8.3 Hz, 2H, Ph).13C NMR (CDCl3, d, ppm): 12.91, 13.20
(CH3), 47.41, 47.83 (N–CH2), 127.70, 127.78, 128.45, 128.65,
130.94, 131.76, 132.10 and 134.98(Ph), 166.69 (C@N),
172.70(C@S), 173.73 (C@O).
4.5.3. [ReO(L)(R1R2btu)] (6)
Method 1. [ReO(L)Cl] (59 mg, 0.1 mmol) was dissolved in CH2Cl2
(10 mL). HR1R2btu (0.1 mmol) and three drops of NEt3 were added
under stirring. The red colored solution was heated under reflux for

2 h and the solvent was removed under vacuum to dryness. The
resulting residue was either washed with cold MeOH or recrystallized from CH2Cl2/MeOH to give red crystalline products.
Method 2. A mixture of H2L (35 mg, 0.1 mmol) and HR1R2btu
(0.1 mmol) in 3 mL acetone was added to a solution of (NBu4)
[ReOCl4] (58 mg, 0.1 mmol) in 3 mL CH2Cl2. After stirring at room
temperature for 10 min, three drops of NEt3 were added and the
mixture was heated under reflux for 2 h. This resulted in the formation of a dark red solution. The solvent was removed in vacuo
and the residue was treated as described in method 1.

4.5. Syntheses of complexes

4.5.4. Data for [ReO(L)(Ph2btu)] (6a)
Yield: 63% (56 mg) for method 1, 71% (63 mg) for method 2.
Anal. Calc. for C39H35N6O3S2Re: C, 52.86; H, 3.98; N, 9.48; S, 7.24.
Found: C, 52.00; H, 3.25; N, 9.37; S, 6.93%. IR (m in cmÀ1):
3055(w), 2978(w), 2924(w), 1512(vs),1450(s), 1427(vs), 1404(vs),
1334(m), 1257(m), 972(s), 694(s). 1H NMR (CDCl3; d, ppm): 1.23
(t, 3H, CH3), 1.25 (t, 3H, CH3), 3.74 (m, 2H, CH2), 3.91 (m, 1H,
CH2), 4.00 (m, 1H, CH2), 6.99(t, J = 7.9 Hz, 2H, Ph), 7.2–7.4(m,
19H, Ph), 7.79(d, J = 8.4 Hz, 2H, Ph), 7.99(d, J = 8.4 Hz, 2H, Ph). 13C
NMR (CDCl3; d, ppm): 13.35 (CH3), 13.38 (CH3), 46.58 (CH2),
47.49 (CH2), 127–136 (Ph), 163.20 (C@N, L2À), 173.10 (C@S,
Ph2btuÀ), 174.05 (C@S, L2À), 176.18 (C@O, L2À), 186.95 (C@O,
Ph2btuÀ). FAB+ MS (m/z): 909, 11%, [M+Na]+; 887, 40%, [M+H]+;
814, 6%, [MÀNEt2]+; 692, 65%, [MÀPh2NC„N]+.

4.5.1. [TcO(L)Cl] (4)
H2L (42 mg, 0.12 mmol) dissolved in 2 mL MeOH was added
dropwise to a stirred solution of (NBu4)[TcOCl4] (58 mg, 0.1 mmol)
in 1 mL MeOH. The color of the solution immediately turned deep

red and a red precipitate deposited within a few minutes. The red
powder was filtered off, washed with cold methanol and dried under vacuum. X-ray quality single crystals of 4 were obtained by
slow evaporation of a dichloromethane/methanol solution. Yield:
50% (26 mg). Anal. Calc. for C19H20ClN4O2STc: Tc, 20.8. Found: Tc,
20.7%. IR (m in cmÀ1): 3055(w), 2985(w), 2932(w), 2870(w),
1504(vs), 1434(m), 1389(s), 1354(m), 1327(m), 1292(m),
1174(w), 1095(w), 1064(w), 1026(w), 976(s), 775(m), 698(s). 1H
NMR (CDCl3; d, ppm): 1.30 (t, J = 7.1 Hz, 3 H, CH3), 1.37 (t,
J = 7.1 Hz, 3 H, CH3), 3.90–4.00 (m, 4 H, CH2), 7.32 (t, J = 7.4 Hz, 2
H, Ph), 7.36 (t, J = 6.9 Hz, 1 H, Ph), 7.42 (t, J = 7.7 Hz, 2 H, Ph),

4.5.5. Data for [ReO(L)(morphbtu)] (6b)
Yield: 40% (32 mg) for method 1, 59% (47 mg) for method 2.
Anal. Calc. for C31H33N6O4S2Re: C, 46.31; H, 4.14; N, 10.55; S,
7.98. Found: C, 46.22; H, 4.04; N, 10.40; S, 8.12%. IR (m in cmÀ1):
3062(w), 2978(w), 2926(w), 1520(vs),1488(vs), 1420(vs), 1350(s),
1311(s), 1234(m), 1110(m), 1065(m), 1026(m), 972(s), 771(m),
694(s). 1H NMR (CDCl3; d, ppm): 1.23 (t, 3H, CH3), 1.25 (t, 3H,
CH3), 3.74 (m, 2H, morphNCH2), 3.89 (m, 2H, morphNCH2), 3.95–
4.05 (m, 4H, NCH2), 4.29 (m, 1H, morphOCH2), 4.34 (m, 1H, morphOCH2), 4.46 (m, 1H, morphOCH2), 4.58 (m, 1H, morphOCH2),
7.09 (t, J = 7.7 Hz, 2H, Ph), 7.21–7.27(m, 4H, Ph), 7.34–7.41 (m,
3H, Ph), 7.68(d, J = 7.1 Hz, 2H, Ph), 7.81(d, J = 8.3 Hz, 2H, Ph), 7.90
(d, J = 8.3 Hz, 2H, Ph). 13C NMR (CDCl3; d, ppm): 13.37 (CH3),
13,40 (CH3), 46.59 (NCH2), 47.57 (NCH2), 48.32 (NCH2), 49.81
(NCH2), 67.12 (OCH2), 67.34 (OCH2), 127.37, 127.72, 127.96,


3951

H.H. Nguyen, U. Abram / Polyhedron 28 (2009) 3945–3952

Table 4
X-ray structure data collection and refinement parameters.

Formula
Mw
Crystal system
a (Å)
b (Å)
c (Å)
a (°)
b (°)
c (°)
V (Å3)
Space group
Z
Dcalc (g cmÀ3)
l (mmÀ1)
No. of reflections
No. of independent
No. of parameters
R1/wR2
Goodness-of-fit (GOF)
CSD deposit number

H2L

[TcOCl(L)] (4)

[ReOCl(L)] (5)

[ReO(L)(Ph2btu)] (6a)

[ReO(L)(morphbtu)] (6b)

C19H22N4OS
354.48
orthorhombic
15.496(3)
14.953(2)
15.847(2)
90
90
90
3671.9(10)
Pbca
8
1.282
0.191
9423
4744
249
0.0505/0.0886
0.741
CCDC-728398

C19H20ClN4O2STc
501.90
monoclinic
12.148(1)
12.886(1)

13.126(1)
90
98.02(1)
90
2034.6(3)
P21/n
4
1.639
0.964
16 151
5473
254
0.0288/0.0618
0.948
CCDC-728400

C19H20ClN4O2ReS
590.10
monoclinic
9.718 (1)
13.510(1)
15.564(1)
90
95.28(1)
90
2034.7(3)
P21/n
4
1.926
6.229

15 294
5483
254
0.0749/0.1676
0.916
CCDC-728399

C39H35N6O3ReS2
886.05
monoclinic
15.940(5)
13.429(5)
18.565(5)
90
111.56(1)
90
3696(2)
Cc
4
1.592
3.447
13 016
7280
461
0.0534/0.1268
1.086
CCDC-728401

C31H33N6O4ReS2
803.95

triclinic
9.547(5)
10.245(5)
16.751(5)
105.03(1)
90.08(1)
97.66(1)
1567(1)

P1

128.48, 129.56, 129.80, 130.42, 130.67, 131.44, 132.01, 135.42 and
136.47 (Ph), 163.25 (C@N, L2À), 171.99 (C@S, morphbtuÀ), 173.93
(C@S, L2À), 176,19 (C@O, L2À), 184.85 (C@O, morphbtuÀ). FAB+
MS (m/z): 827, 9%, [M+Na]+; 805, 38%, [M+H]+; 692, 37%, [MÀmorphC„N]+; 572, 35%, [ReO2(L2À)]+.
4.6. X-ray crystallography
The intensities for the X-ray determinations were collected on a
STOE IPDS 2T instrument with Mo Ka radiation (k = 0.71073 Å).
Standard procedures were applied for data reduction and absorption correction. Structure solution and refinement were performed
with SHELXS97 and SHELXL97 [22]. Hydrogen atom positions were calculated for idealized positions and treated with the ‘riding model’
option of SHELXL. More details on data collections and structure calculations are contained in Table 1.
Additional information on the structure determinations has
been deposited with the Cambridge Crystallographic Data Centre
(see Table 4).
Supplementary data

[6]

[7]
[8]

[9]

[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]

CCDC 728398, 728399, 728400, 728401 and 728402 contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge via />retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336033; or e-mail:
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